Effect of Cryo-Suction and Air Void Transition Layer on Hydraulic Pressure of Freezing Concrete

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Title: Effect of Cryo-Suction and Air Void Transition Layer on Hydraulic Pressure of Freezing Concrete

Author(s): Paulo J. M. Monteiro, Olivier Coussy, and Denise A. Silva

Publication: Materials Journal

Volume: 103

Issue: 2

Appears on pages(s): 136-140

Keywords: cracking; shells; shrinkage; voids.

Date: 3/1/2006

Abstract:
Advanced scanning electron microscopy methods were used to characterize the microstructure of cement paste containing entrained air voids. Environmental electron microscopy allowed the imaging of the cement paste without exposing it to high vacuum, therefore significantly eliminating the risk of shrinkage cracks. The fine details of the air-void shell were resolved using field emission microscopy. Finally, ice crystals inside the air-void were imaged using low-temperature scanning electron microscopy. These microscopy studies showed the presence of a transition layer surrounding the air void, which can have a significant effect on the ice formation inside the air voids. The microscopic analysis seems to confirm that the entrained air voids also cause cryo-suction by driving the liquid water from the cement paste during freezing. Both observations are included in a mathematical model that extends the original Powers’ model for freezing of concrete.